Method and means for stabilizing amplifiers



' mzww May 17 9 9 E H. LANGE METHOD AND MEANS FOR STABILIZING AMPLIFIERS Filed Aug. 28, 1925 k333i L T 'N' 9 lg IN VEN TOR A ITORNEY Patented May 17, 1927.

' UNITED STATES 'nnwnnn 1;. men, or NEW Yonx, 11. 2.

FFICE.

PATENT-Q a u mmnea August a. 1925. sci-x5116. $3,002.

vThis invention relates to thermionic amplifiers and has particular reference to means for amplifying radio frequencysignals in a multi-stage thermionic amplifier without troublesome regeneration normally encountered in the individual stages due to unavoidable c'a acity between the electrodes of the thermionic tubes. In multi-stage tuned radio frequency amplifiers, unbalanced magnetic or capacitive coupling be- 5 gized by means of the antenna 1, and conrate stages results in lack of independence.

tween input and output circuits of the sepaof tuning of the separate stages, which is detrimental tothe" uniformity and duplication ofcondenser settings for a particular signal frequency, and results also 1n poor quality reproduction of the received signal.

The object of this invention is to provide simple method and means whereby inherent and extraneous capacitive coupling between grid and plate of the thermionic tubes of the separate sta es of 'a multi-stage amplifier can be exact y balanced over a range of frequencies, and energy transfer from the output to the input elements of the separate stages prevented. In a multi-stage thermionic amplifier, coupling normally exists between the input and output elements ofthe separate stages, which is either ma etic or capacitive or both. By means 0 this I coupling energy is fed back from the output elements to'the input elements,'whi ch gives rise to increased amplification, but 1ntroduces'irregularities in the tuning of the similar separate stages, which independently tune at the same settings. When the energy fed back due-to mutual reactance between the input and output elements of the thermionic tube is sufiicient to'overcome the circuit losses,self sustained oscillations are produced within the amplifier which interfere with the amplified impressed signal. The magnetic coupling between input and output elements of the individual stages can be eliminated by proper shielding of th nag netic elements of the circuit, or proper orientation of the magnetic elements- The present'invention deals with a method for annulling the eleetromotive forces impressed" upon the input circuits of the separate stages from the respective output circuits due to inherent and extraneous capacity which ex-- ists between the input and output elements of, the thermionic tubes of the separate stages. Y

Beferringto the accompanying drawings;

Fig. 1' shows diagrammatically a four stage amplifier and. detector with an embodi ment of my invention applied thereto.

Fig. 2 illustrates in diagram form the method of stabilizing the amplifier shown in Fig. 1.

Referring in particular to Fig.1 a direct coupled tuned radio, frequency amplifier havmg'four tuned'stages and a detector-is shown. Grid 5 of the first stage is enerpled circuit 2, 3, or directly by the tuned circuit 2, 3, alone.- The output impedance .of the first tube consists of a tuned circuit 8, 9,in series with a condenser 7. The capacity of the condenser 7, is sufiiciently large to make the Volta e drop across 7, small compared with the rep across the tuned circuit 8, 9. .The' condenser 7, serves to keep the steady plate potential from the grid 11, the alternating component of plate current being confined to the output circuit 6, 7, 8, 9,

17, 23, and 24, perform a function similar to condenser 7 Due to the inter-electrode capacity 5, 6, the input circuit 2, 3, is not independent of the output circuit 6, 7, 8, 9, 4, but together with the capacity 5, 6, in series,

the input circuit 2, 3, is shunted across the output circuit. Normally, when the circuits 2, 3, and 8, 9, are very nearly in tune for a certain frequency, the resultant reactance of each of these circuits is inductive, and relatively large compared with the reactance of the individual inductance coils alone, and

the voltage drop across 2, 3, due to its shunt connection across'the output inductive reactance 7, 8, 9, through the relatively high capacity reactance- 5, 6, is in proper phase to. reinforce the'current in the output circuit." ThlS process gives rise to regeneration, or to self sustained oscillations if sufiicient energy .is fed back from the output to the input circuitto overcome the circuit losses. In the direct .couplmg used between the stages or in other forms of con ling between the output circuit of any tu e and the input cir-- cuit of the following tube, a phase reversal is obtained between the output circuits of successive tubes.- The alternating voltage drop across 16, 15, is substantially 180 out of phase with the drop across 8, 9, and

largeii the drop across 8, 9, in proper- 'across 8, 9.

tionf-to the resultant amplification of the intervening tube. By means of the connection 14, a voltage drop across 14, 15, is obtained which is substantially equal in magnitude and opposite inphase to the drop.

lhe voltage across l4, 15, is applied to the grid 5, by means of a stabilizing condenser 12, thereby reducing the voltage across 2, '3, due to reaction ofthe outputcircuit 6, 7, 8, 9, 4, to zero. The stabilizing condensers and'22, perform a function similar to condenser 12. I Thebalancingcircuit can be better understood by reference to Fig. 2. The voltage drops-across the circuits 7, 8, 9, and 14, 15,

are represented by: synchornous alternators haying equal and opposite electromotive force, and connected to the common point 4,

which is thef'common filament connection of thejtubesin Fig. 1. The interelectrode' capacity 5, 6, and stabilizing-capacity 12,

form a closed circuit across the terminals 6,

scribed is not restricted to this method of energy supply. Manifestly energy may be drawn from any other suitable source such as a battery eliminator or the like. larmanner it will be understood that many other changes and modifications in the specific embodiment shown may be made within the scope of my invention and the .spirit of the appended claims.

What I claim is: p

. 1. The method of preventing regeneration in a conductively coupled amplifier provided with a plurality of subsidiary amplifying .,means having, tuned inp'ut circuits, tuned output circuits, and inherent capacity between said circuits, which comprises inserting capacitance between the input circuit of one said means and the output circuit of another said means and thereby impressing upon the first said input circuit electromotive force substantially equal and opposite to that impressed upon said input circuit fromthe output circuit of said first means through said inherent capacity.

2. The method of preventing regeneration inacon'ductively coupled amplifier embodying a series of amplifying means each having a tuned input circuit, a tuned output circuit, and inherent capacity between said circuits, which comprises inserting capacia; tance between said input circuit of one said means and the output circuit of the succeed- In simiing said means, and through. the medium of said capacitance impressing upon the first said means input circuit an electromotive force component opposing that impressed upon said first means input circuit from the first means output circuit.

3. Ina thermionic amplifier having a plurality of stages each provided with a tuned input circuit, a tuned output circuit, inherent capacity between said circuits, a continuous current anode energizing clrcult containing a choke'coil; and a conductive connection from said stage output circuit to the succeeding'stage input circuit; a condenser separat ing said anode energizing circuit and said succeeding stage inputcircuit, said condenser preventing said continuous current from the anode energizing circultfiowing to said succeeding stage input circuit, and a stabilizing condenser connectedfrom the first said stage input circuit to a point in said succeeding stage tuned output circuit,

whereby an electromotive force of substantially equal magnitude and opposite phase to that applied to the first said stage input circuit through said inherent capacity from saidoutput circuit of said first stage is applied to said input circuit. I

4.- In a stabilizer for thermionic amplifiers having a plurality of stages each including a tube having a cathode, anode, control electrode, inherent capacity between electrodes,

a conductive coupling between the tuned output circuit of one said stage and the following stage control electrode, and an anode energizing circuit containing a high impe'dtwcen each anode and the tuned output circuit of the same stage, said condenser serving to prevent the flow of continuousrurrent from said anode to the control electrode of the following stage, and a stabilizing conlowing stage tuned output circuit, said stabilizing condenser serving to impress upon the control electrode a reactive voltage drop of opposite phase to the voltage impressed upon said control electrode from the anode of the same stage by reason of said inherent capacity.

5. The combination in a thermionic multistage amplifier each of whose stages include a cathode, anode, control electrode, inherent capacity between electrodes, and .a continuous current anode energizing circuitincludmg a choke coil, a single tuned circuit between said stages and common to the output'circuit of one stage and the input circuit of the following stage, a separating condenser connccted between each stage anode of continuous current from said anode to the following stage control electrode, and a staance choke coil; a condenser connectedbe: 1

bilizirig" circuit including a tabiliz n co n denser connected from" the control electtede of One stage to anfintei'mediat e point on-the ihductive port10n'of the timed out ht-cir- Xzuin of the followin stage, said sta ilizing circuit providing bi; ancingimean s' whei eby the; voltage dropszi'cross -said inclu'ctiw, p0rt'iori bbt'amed by. amplificationfifi the-inter- 'vening 's tag'e is balancii ii gainst thej-iiol t z ig' drop impressed uponfthj contrgil electrqde 10 from the output-circuit bf tl'i e' mpIne stilgel Signedhat. New York, in the countyi'bf v ew Yor kahc'iist ate of-New York, this 27th dayof August; 1925.

- i-ni wk in Ii; LANGE. 

